A regression model was established that relates the lifetime (12/12) warranty repair rate to complexity of passenger car wiring harnesses. Complexity factors were obtained from released design specifications and supplier input which included; (1) the number of connectors to exterior power devices, actuators, switches, and to other wiring harnesses, (2) the number of circuits in the harness, (3) the number of terminals, (4) the number of wiring circuit splices and (5) the length of wire. For the two car lines studied, the correlation between these variables and the lifetime (12/12) repair rates for wiring harness assemblies was high, with correlation coefficients being in the range of .80 -. 91. The repair rates were obtained from an analysis of selected warranty claims with mechanics comments which validated the accuracy of the stated wiring harness failure.High intercorrelation between the complexity factors was found, thus a simple model with as few as two factors (i.e. length of wire and the number of terminals) in the regression equation was sufficient for warranty prediction. Factors such as vehicle location and vehicle type were not concluded to be important in establishing the model; however studies across additional car lines would be required to determine if a true relationship exists.